2005-04-23 18:45:54

by Jesper Juhl

Subject: [PATCH] udf: uint32_t can't be less than zero

Here's a patch that removes a few bits from fs/udf/balloc.c that
test uint32_t values for being less than zero, which is impossible.

I know not everyone agree with this sort of cleanup, but I figured I'd do
the patch in any case, then leave it up to the maintainer to apply it or
drop it.

Please keep me on CC: when replying.



Signed-Off-by: Jesper Juhl <[email protected]>


--- linux-2.6.12-rc2-mm3-orig/fs/udf/balloc.c 2005-03-02 08:37:52.000000000 +0100
+++ linux-2.6.12-rc2-mm3/fs/udf/balloc.c 2005-04-23 20:38:31.000000000 +0200
@@ -158,8 +158,7 @@ static void udf_bitmap_free_blocks(struc
unsigned long overflow;

down(&sbi->s_alloc_sem);
- if (bloc.logicalBlockNum < 0 ||
- (bloc.logicalBlockNum + count) > UDF_SB_PARTLEN(sb, bloc.partitionReferenceNum))
+ if ((bloc.logicalBlockNum + count) > UDF_SB_PARTLEN(sb, bloc.partitionReferenceNum))
{
udf_debug("%d < %d || %d + %d > %d\n",
bloc.logicalBlockNum, 0, bloc.logicalBlockNum, count,
@@ -232,7 +231,7 @@ static int udf_bitmap_prealloc_blocks(st
struct buffer_head *bh;

down(&sbi->s_alloc_sem);
- if (first_block < 0 || first_block >= UDF_SB_PARTLEN(sb, partition))
+ if (first_block >= UDF_SB_PARTLEN(sb, partition))
goto out;

if (first_block + block_count > UDF_SB_PARTLEN(sb, partition))
@@ -299,7 +298,7 @@ static int udf_bitmap_new_block(struct s
down(&sbi->s_alloc_sem);

repeat:
- if (goal < 0 || goal >= UDF_SB_PARTLEN(sb, partition))
+ if (goal >= UDF_SB_PARTLEN(sb, partition))
goal = 0;

nr_groups = bitmap->s_nr_groups;
@@ -439,8 +438,7 @@ static void udf_table_free_blocks(struct
int i;

down(&sbi->s_alloc_sem);
- if (bloc.logicalBlockNum < 0 ||
- (bloc.logicalBlockNum + count) > UDF_SB_PARTLEN(sb, bloc.partitionReferenceNum))
+ if ((bloc.logicalBlockNum + count) > UDF_SB_PARTLEN(sb, bloc.partitionReferenceNum))
{
udf_debug("%d < %d || %d + %d > %d\n",
bloc.logicalBlockNum, 0, bloc.logicalBlockNum, count,
@@ -688,7 +686,7 @@ static int udf_table_prealloc_blocks(str
struct buffer_head *bh;
int8_t etype = -1;

- if (first_block < 0 || first_block >= UDF_SB_PARTLEN(sb, partition))
+ if (first_block >= UDF_SB_PARTLEN(sb, partition))
return 0;

if (UDF_I_ALLOCTYPE(table) == ICBTAG_FLAG_AD_SHORT)
@@ -768,7 +766,7 @@ static int udf_table_new_block(struct su
return newblock;

down(&sbi->s_alloc_sem);
- if (goal < 0 || goal >= UDF_SB_PARTLEN(sb, partition))
+ if (goal >= UDF_SB_PARTLEN(sb, partition))
goal = 0;

/* We search for the closest matching block to goal. If we find a exact hit,

2005-04-24 09:42:47

by Denis Vlasenko

Subject: Re: [PATCH] udf: uint32_t can't be less than zero

On Saturday 23 April 2005 21:48, Jesper Juhl wrote:
> Here's a patch that removes a few bits from fs/udf/balloc.c that
> test uint32_t values for being less than zero, which is impossible.
>
> I know not everyone agree with this sort of cleanup, but I figured I'd do
> the patch in any case, then leave it up to the maintainer to apply it or
> drop it.
>
> Please keep me on CC: when replying.
> - if (bloc.logicalBlockNum < 0 ||
> - (bloc.logicalBlockNum + count) > UDF_SB_PARTLEN(sb, bloc.partitionReferenceNum))
> + if ((bloc.logicalBlockNum + count) > UDF_SB_PARTLEN(sb, bloc.partitionReferenceNum))

It is not immediately visible here that bloc.logicalBlockNum is unsigned.
One needs to check that by looking at the definition.

Also if later someone changes bloc.logicalBlockNum into signed entity, code
becomes buggy. Not good.

gcc already optimizes out such checks:

# gcc -O2 t.c -S -fomit-frame-pointer
# cat t.c t.s
extern unsigned v;

int f() {
return v<0 || v>100 || v==50;
}
.file "t.c"
.text
.p2align 2,,3
.globl f
.type f, @function
f:
movl v, %edx
xorl %eax, %eax
cmpl $100, %edx
ja .L3
cmpl $50, %edx
je .L3
ret
.p2align 2,,3
.L3:
movl $1, %eax
ret
.size f, .-f
.section .note.GNU-stack,"",@progbits
.ident "GCC: (GNU) 3.4.3"
--
vda